Fuel injection system

Abstract

 A throttle body fuel injection system has a pressure regulator (46), (56) which reduces the pressure of the fuel supplied to its electromagnetic injector (42) as the pressure in the engine induction passage (14) decreases.

Description

[0001] This invention relates to a fuel injection system.

[0002] Certain automotive engines are equipped with a low pressure fuel injection system having an electrically energized injector which delivers fuel in timed pulses into the engine air induction passage above the throttle. Such a fuel injection system is currently known as a throttle body injection system, or TBI system. In a system of this nature, fuel flow is controlled by energizing the injector at regular intervals and varying the duration of the fuel delivery pulses: when increased fuel delivery is desired, the injector is energized for a longer period of time to increase the duration of the fuel delivery pulse, whereas when decreased fuel delivery is desired, the injector is energized for a shorter period of time to decrease the duration of the fuel delivery pulse.

[0003] It has been recognised that variations in the pressure of the fuel supplied to the injector also affect fuel delivery by the injector. Accordingly, in order to provide predictable and repeatable fuel delivery by the injector in response to the duration of the fuel delivery pulses, a fuel pressure regulator is employed to maintain a constant fuel supply pressure. The fuel is supplied to the injector by a pump, and the pump supplies more fuel than is required by the injector. The excess fuel is directed through a fuel pressure regulator, for example as disclosed in US-A-3,511,270. The pressure regulator has a diaphragm which balances the pressure of the fuel supplied to the injector with the bias of a pressure regulator spring. If the pressure of the fuel supplied to the injector is less than the spring bias, the diaphragm positions a valve to shut off the excess fuel flow and thus increase the fuel pressure at the injector; if the pressure of the fuel supplied to the injector exceeds the spring bias, the diaphragm retracts the valve to discharge the excess fuel and thus reduce the fuel pressure at the injector.

[0004] It is evident, therefore, that the fuel pressure at the injector is determined by the bias of the pressure regulator spring, and the desired fuel pressure is established by adjusting the bias of the spring.

[0005] The fuel flow orifice in an electrically energized injector must be large enough to deliver the maximum fuelflow required by the engine when the injector is continuously energized. Preferably the fuel flow orifice is sized to deliver the maximum quantity of fuel required for any pulse when the injector is energized for a period of time which is 90% of the pulse-to-pulse interval -- that is, the maximum quantity of fuel is delivered when the injector is energized with a 90% duty cycle. Then when a lesser quantity of fuel is required, the injector is energized with a proportionally lesser duty cycle. Thus the size of the fuel flow orifice establishes the duty cycle which will deliver the minimum quantity of fuel required for a pulse occuring during an operating condition such as engine deceleration. For example, an increase in the size of the fuel flow orifice necessary to increase the maximum quantity of fuel delivered by the injector is accompanied by a decrease in the duty cycle employed to deliver a specified minimum quantity of fuel in each pulse.

[0006] However, an electrically energized injector must be energized for at least a minimum period of time in order to be in a position to deliver a predictable and repeatable quantity of fuel in each pulse. Clearly, care is needed to avoid a situation in which the duty cycle employed to deliver the minimum quantity of fuel produces a pulse duration which is less than the minimum period of time required to deliver a predictable and repeatable quantity of fuel.

[0007] It would in principle be possible for the fuel flow orifice to be sized so that the minimum quantity of fuel required for any pulse would be delivered in the minimum period of time required for a predictable and repeatable fuel pulse. However, such calibration would limit the maximum quantity of fuel which could be delivered in the maximum pulse duration.

[0008] Overall, the fuel flow available from prior fuel injection systems employing electrically energized injectors has been limited by the size of the fuel flow orifice and by the minimum pulse duration.

[0009] The present invention takes as its starting point a fuel injection system as disclosed in SAE Technical Paper 800164, which discloses a fuel injection system for an engine having an induction passage for air flow to the engine and a throttle in the induction passage for controlling air flow therethrough, the fuel injection system comprising an electrically energizable fuel injector adapted to deliver timed pulses of fuel into a region of the induction passage, a control unit for energizing the injector and adapted to establish the duration of the pulses and the interval between the pulses, a fuel passage for supplying fuel to the injector, and a pressure regulator for controlling fuel flow through the fuel passage, the pressure regulator including a diaphragm overlying a base and defining a fuel chamber therebetween, the base having a fuel access region opening from the fuel passage to the chamber and a fuel outlet opening from the chamber and a valve seat surrounding the outlet, the diaphragm carrying a valve member for controlling fuel flow past the valve seat through the outlet, a spring engaging the diaphragm to bias the diaphragm to urge the valve member towards the valve seat, and a housing overlying the diaphragm and defining a bias pressure chamber therebetween.

[0010] The invention is concerned with increasing the fuel flow available from such a fuel injection system without affecting either the size of the fuel flow orifice or the minimum pulse duration.

[0011] To this end, a fuel injection system in accordance with the present invention is characterised in that the system further comprises means for subjecting the bias pressure chamber to the pressure in the induction passage downstream of the throttle to thereby further bias the diaphragm to urge the valve member towards the valve seat, whereby fuel flow past the valve seat through the outlet is controlled to balance the fuel pressure on the diaphragm with the combination of the bias of the spring on the diaphragm and the bias of the pressure in the induction passage on the diaphragm, such that the fuel injection system thereby decreases the difference between the pressure of the fuel supplied to the injector and the pressure in the said region as the induction passage pressure decreases, to thereby decrease the fuel delivery capacity of the injector as air flow decreases.

[0012] In a specific embodiment of a fuel injection system in accordance with the present invention, the fuel pressure regulator is biased by a pressure signal from the engine induction passage. The pressure signal is lowest under minimum engine air flow conditions and highest under maximum engine air flow conditions, and causes the pressure regulator to reduce the pressure of the fuel supplied to the injector as the engine air flow decreases. The fuel flow orifice is sized so that the maximum quantity of fuel required for any pulse is delivered in the maximum pulse duration; however, that calibration does not establish the duty cycle which will deliver the minimum quantity of fuel required-for any pulse, but rather the reduced fuel supply pressure requires a substantially increased duty cycle to deliver the minimum quantity of fuel required for any pulse.

[0013] Thus in a fuel injection system in accordance with the present invention, the fuel flow orifice may be sized to deliver the maximum quantity of fuel required for any pulse in the time available for that pulse, and yet the duty cycle employed to deliver the minimum quantity of fuel required for any pulse may be such as will produce a pulse duration which is greater than the minimum period of time required to deliver a predictable and repeatable quantity of fuel.

[0014] The single Figure of the drawing schematically illustrates a preferred embodiment of a throttle body fuel injection system in accordance with the present invention.

[0015] As is shown in the drawing, a throttle body fuel injection system in accordance with the present invention includes a throttle body injection (TBI-) assembly 10. The TBI assembly 10 includes a throttle body 12 having an air induction passage 14 forming a portion of the engine air induction system and controlled by a throttle 16.

[0016] A fuel body 18 is mounted on the throttle body 12. The fuel body 18 includes an inlet 20 adapted to receive fuel from a low pressure supply pump, and an excess fuel outlet 22 is formed in a fuel body cover 23.

[0017] Within the fuel body 18, a passage 26 directs fuel to an injector chamber 28, and a passage 30 opens from the injector chamber 28 to an intermediate chamber 32 defined between the fuel body 18 and its cover 23. A pressure regulator access region 34 opens from the intermediate chamber 32 to a pressure regulator chamber 36 which discharges through a passage 38 to the excess fuel outlet 22.

[0018] A bypass 40 opens from the passage 26 to the intermediate chamber 32, thereby allowing any fuel vapour present in the passage 26 to bypass the injector chamber 28.

[0019] From the foregoing, it will be evident that the fuel flow path extends from the inlet 20 through the passage 26, injector chamber 28, passage 30, intermediate chamber 32, access region 34, pressure regulator chamber 36 and passage 38 to the excess fuel outlet 22. Fuel circulating through this path cools the fuel body 18 to maintain the TBI system below temperatures at which fuel vapour might otherwise be generated.

[0020] An electromagnetic injector 42 is mounted in the injector chamber 28 for energization in a conventional manner by an electronic control unit 43 to deliver fuel in timed pulses from the injector chamber 28 into the region of the air induction passage 14 above the throttle 16. In order that the injector 42 may deliver a predictable and repeatable amount of fuel to the air induction passage 14 in response to variations in the duration of the timed pulses, a desired supply pressure is established in the injector chamber 28. To this end, the fuel body cover 23 forms a base for a pressure regulator diaphragm 44 which closes the pressure regulator chamber 36 and carries a pressure regulator valve 46. A spring 48 biases the pressure regulator diaphragm 44 and valve 46 upwardly towards a position of engagement of the valve 46 with a valve seat 50 formed about the portion of the fuel flow path opening from the pressure regulator chamber 36 to the passage 38. Should the supply pressure in the pressure regulator chamber 36, and thus in the injector chamber 28, rise above the desired supply pressure, the diaphragm 44 is displaced downwardly against the bias of the spring 48 to pull the valve 46 away from the valve seat 50: additional fuel is thereby permitted to flow from the pressure regulator chamber 36 to the passage 38 to reduce the supply pressure in the pressure regulator chamber 36 and the injector chamber 28. Should the supply pressure in the pressure regulator chamber-36 and injector chamber 28 fall below the desired supply pressure, spring 48 displaces the diaphragm 44 upwardly to push the valve 46 towards the valve seat 50, whereby fuel flow from the pressure regulator chamber 36 to the passage 38 is reduced to increase the supply pressure in the pressure regulator chamber 36 and injector chamber 28. Under steady state conditions, with the desired pressure. in the pressure regulator chamber 36, the diaphragm 44 will position the valve 46 somewhat away from the seat 50, so allowing a continuous flow of fuel through the fuel body 18.

[0021] A spring housing 52 surrounds the spring 48 to define a bias pressure chamber 54 below the diaphragm 44. The chamber 54 is connected by way of a valve assembly 56 to the induction passage 14 at a position downstream of the throttle 16.

[0022] Within the valve assembly 56 a diaphragm valve member 58 is associated with a valve seat 60 to control communication between a fitting 62 connected to the induction passage 14 and a chamber 64 connected by means of a fitting 66 to the bias pressure chamber 54. A spring 68 urges the diaphragm valve member 58 away from the valve seat 60 to place the sub-atmospheric induction passage pressure (also known as manifold pressure) from the induction passage 14 in communication by way of the chamber 64 with the bias pressure chamber 54.

[0023] When the pressure in the chamber 64 -- and thus in the bias pressure chamber 54 -- drops below the predetermined setting of the spring 68, the diaphragm valve member 58 encaces the seat 60 to thereby establish a lower limit for the pressure applied to the bias pressure chamber 54. A restricted air bleed 70 opens into the chamber 64 to gradually increase the pressure in the chamber 64. Thus when the induction passage pressure is below the setting of the spring 68 (that is, when the manifold vacuum is above the setting of the spring 68), the diaphragm valve member 58 will cycle on and off the seat 60 to maintain the pressure in the chamber 64 and in the bias pressure chamber 54 at the predetermined lower limit established by the spring 68.

[0024] When the induction passage pressure rises above the setting of the spring 68 (that is, when the manifold vacuum drops below the setting of the spring 68), the spring 68 displaces the diaphragm valve member 58 from the seat 60, and the bias pressure chamber 54'is thereby subjected to the induction passage pressure.

[0025] The pressure in the induction passage 14 below the throttle 16 varies with engine air flow, and is lowest at the lowest engine air flow and highest at the highest engine air flow. The application of induction passage pressure to the bias pressure chamber 54 accordingly reduces the upward bias on the pressure regulator diaphragm 44 as engine air flow decreases. In response, the diaphragm 44 positions the valve 46 to reduce the fuel supply pressure as the engine air flow decreases. The reduced fuel supply pressure decreases the quantity of fuel which the injector 42 can deliver in any particular pulse duration.

[0026] The electronic control unit 43 responds to signals such as engine speed and induction passage pressure, which together represent air flow through the induction passage 14, and energizes the injector 42 to deliver fuel in pulses which are timed to provide the desired mixture of air and fuel. With the present system in accordance with the invention, the electronic control unit 43 must prolong the injector energization period to compensate for the change in the fuel supply pressure: when the electronic control unit 43 has a memory addressed by engine speed and induction passage pressure to establish the period of time for which the injector 42 is to be energized, the time periods corresponding to induction passage pressures above the lower limit established by the valve assembly 56 are extended to compensate for the change in the fuel supply pressure. Then as the fuel supply pressure is reduced with engine air flow, the electronic control unit 43 increases the duty cycle over what would otherwise be called for, to thereby deliver the quantity of fuel required for any pulse.

[0027] Thus this invention allows an increase in the duty cycle employed to deliver the minimum quantity of fuel in any pulse, and thereby ensures that the minimum quantity of fuel required for any pulse is delivered in a period of time which can produce a predictable and repeatable amount of fuel.

[0028] The valve assembly 56 establishes a lower limit for the pressure applied to the bias pressure chamber 54, and thereby ensures that the fuel supply will be maintained at or above the pressure required for proper fuel delivery by the injector 42.

[0029] This invention has been described with reference to a system in which the injector is energized at regular intervals for a period of time which may be varied -- that is, a pulse width modulated system. The frequency of injection is preferably varied to coincide with the frequency of the combustion events in the engine, and thus increases with engine speed. This invention could alternatively be employed in a system in which the injector is energized for a fixed period of time at intervals which are reduced as the fuel flow requirement increases -- that is, a frequency modulated system.

[0030] Moreover, this invention could if required be employed in a fuel injection system having an atmospherically vented injector which delivers fuel through a region of atmospheric pressure into the engine induction system at the combustion chamber inlet port instead of through a region of atmospheric pressure above the throttle as shown in the drawing.

[0031] As described above, the fuel injector system in accordance with the present invention is employed to vary the pressure of the fuel supplied to an injector which delivers timed pulses of fuel into a region of atmospheric pressure; accordingly, the described system achieves its objective by reducing the difference between the fuel supply pressure and the injector discharge pressure as engine air flow decreases. However, a fuel injection system in accordance with the present invention could alternatively be employed in a fuel injection system having an injector which delivers fuel directly into the engine induction system at the combustion chamber inlet port. Such a system conventionally has a pressure regulator bias chamber connected to the air induction system downstream of the throttle to maintain a constant difference between the fuel supply pressure and the injector discharge pressure: by the use of the present invention the fuel supply pressure in such a system would be reduced at a greater rate than the induction passage pressure, to reduce the difference between the fuel supply pressure and the injector discharge pressure as engine air flow decreases.

Claims

1. A fuel injection system for an engine having an induction passage (14) for air flow to the engine and a throttle (16) in the induction passage for controlling air flow therethrough, the fuel injection system comprising an electrically energizable fuel injector (42) adapted to deliver timed pulses of fuel into a region of the induction passage, a control unit (43) for energizing the injector and adapted to establish the duration of the pulses and the interval between the pulses, a fuel passage (26)- for supplying fuel to the injector, and a pressure regulator (46) for controlling fuel flow through the fuel passage,: the pressure regulator including a diaphragm (44) overlying a base (23) and defining a fuel chamber (36) therebetween, the base having a fuel access region (34) opening from the fuel passage to the chamber and a fuel outlet opening (22) from the chamber and a valve seat (50) surrounding the outlet, the diaphragm carrying a valve member (46) for controlling fuel flow past the valve seat through the outlet, a spring (48) engaging the diaphragm to bias the diaphragm to urge the valve member towards the valve seat, and a housing (52) overlying the diaphragm and defining a bias pressure chamber (54) therebetween, characterised in that the system further comprises means (62, 64, 66) for subjecting the bias pressure chamber (54) to the pressure in the induction passage (14) downstream of the throttle (16) to thereby further bias the diaphragm (44) to urge the valve member (46) towards the valve seat (50), whereby fuel flow past the valve seat through the outlet is controlled to balance the fuel pressure on the diaphragm with the combination of the bias of the spring (48) on the diaphragm and the bias of the pressure in the induction passage on the diaphragm, such that the fuel injection system thereby decreases the difference between the pressure of the fuel supplied to the injector and the pressure in the said region as the induction passage pressure decreases, to thereby decrease the fuel delivery capacity of the injector as air flow decreases.

2.. A fuel injection system according to claim 1, characterised in that the said balancing of the fuel pressure is effective to reduce the pressure of the fuel supplied to the injector as the induction passage pressure decreases.

3. A fuel injection system according to claim 1 or 2, characterised in that the injector (42) is arranged to deliver the timed pulses of fuel into a region of substantially constant pressure in the induction passage (14).

4. A fuel injection system according to any one of claims 1 to 3, characterised in that the means (62, 64, 66) for further biasing the diaphragm (44) to urge the valve member (46) towards the valve seat is effective to apply to the bias pressure chamber (54) a pressure signal created in the induction passage downstream of the throttle (16), and that means (56) is effective to establish a lower limit for the pressure signal applied to the bias pressure chamber, to thereby reduce the pressure of the fuel supplied to the injector (42) as the induction passage pressure decreases above the lower limit.

Drawing